1. Field of the Invention
The present invention relates to a vehicular radar system.
2. Description of Related Art
JP-A-2004-177350 describes a vehicular radar system having a light emitter for emitting a laser light and a photoreceptor for receiving a reflected light of the laser light. The vehicular radar system is attempting to improve detection sensitivity of the reflected light reflected by a reflection object.
The light emitter of the vehicular radar system generates the laser light with a laser diode and changes an emission direction of the laser light with a polygon mirror that is driven to rotate. Thus, the light emitter performs scanning over a predetermined angular range for each predetermined minute angle with the laser light. If the laser light is reflected by the reflection object, the photoreceptor receives the reflected light with a light receiving lens. The received light is introduced to photoreceptive elements. The photoreceptive elements output voltage signals corresponding to intensity of the received light.
The vehicular radar system integrates a predetermined number of light reception signals, which are output based on a predetermined number of laser lights emitted contiguously, and outputs an integration signal, while ensuring angular resolution of the laser light. Thus, a light reception signal component corresponding to the reflected light is amplified by integrating the predetermined number of the light reception signals, and detection sensitivity of the reflected light can be improved.
Another vehicular radar system has a light emitter for emitting a laser light over a predetermined angular range in one emission and a photoreceptor having photoreceptive elements of the number corresponding to necessary angular resolution. The photoreceptive elements are arranged into an array along a width direction of the vehicle. This vehicular radar system integrates light reception signals, which are output when the photoreceptive element repeatedly receives the light, for each photoreceptive element. Thus, this vehicular radar system attempts to improve the detection sensitivity of the reflected light.
In such a case where the photoreceptor has multiple photoreceptive elements, usually, a structure shown in FIG. 11A having an integrator that integrates the light reception signals output by the photoreceptor is used.
The structure shown in FIG. 11A includes an amplification circuit (AMP), an A/D conversion circuit (A/D), an integrator, and switches (SW). The amplification circuit AMP amplifies the light reception signals output by the photoreceptive elements (PD) such as photo diodes. The A/D conversion circuit A/D converts the analog light reception signals into digital signals. The integrator integrates the digital light reception signals. The switch SW switches the output of the light reception signal output by each photoreceptive element PD. The amplification circuit AMP, the A/D conversion circuit A/D and the integrator are commonly used for the respective photoreceptive elements PD and switches SW.
The integration of the light reception signals is performed by switching each photoreceptive element PD. Therefore, the integration of the light reception signals output from the respective photoreceptive elements PD cannot be processed at the same time (in parallel). In such a case, the laser light needs to be emitted repeatedly for the time corresponding to the product of the number of the photoreceptive elements PD and the time of the integration. The laser diode will be degraded sooner as the time number of laser light emission increases.
In order to overcome this problem, the amplification circuit AMP, the A/D conversion circuit A/D and the integrator may be disposed for each photoreceptive element PD, without employing the switches SW as shown in FIG. 11B. Thus, the integration of the light reception signals output from the respective photoreceptive elements PD can be performed in parallel, and the early degradation of the laser diode can be inhibited. However, the circuit structure becomes complicated.